Prevention of foot ulcer should result in a reduction in the risk of lower limb amputation. We propose to identify risk factors for diabetic foot ulcer by studying the relationship between endothelial dysfunction and foot ulcer risk. It has been proposed that impaired vasoregulation in diabetic patients leads to the development and perpetuation of chronic foot ulceration via failure of the normal hyperemic response to injury. A fundamental defect that has been demonstrated in type 1 and 2 diabetic subjects is impaired vasodilatory reserve, which reflects dysfunction of endothelium-dependent vasodilation. Our findings thus far point to an important role of the microvasculature in the development of diabetic foot ulcer and amputation, with our demonstration of higher foot ulcer and lower-limb amputation risk in relation to lower dorsal foot transcutaneous oxygen level. The role of endothelial dysfunction in relation to diabetic foot ulcer risk has not previously been studied.